4 MENDELIAN SEGREGATION 
by means of the manceuvers of the chromosomes 
seems to have occurred to more than one person, 
but W. Sutton (1902) first presented the idea in 
the form in which we recognize it today. More- 
over, he not only called attention to the fact above 
mentioned, that both chromosomes and hereditary 
factors undergo segregation, but showed that if 
the pairs assort independently, Mendel’s second law 
(‘‘assortment”’) is fulfilled. Mendel had found that 
when the inheritance of more than one pair of factors 
is followed, the different pairs of factors sort out 
independently of one another. , Thus in a cross of a 
pea having both green seeds and tall stature with a 
pea having yellow seeds and short stature, the fact 
that a germ cell receives a particular member of one 
pair (e.g., yellow) does not determine which member 
of the other pair it receives; it is as likely to receive 
the tall as the short. Sutton pointed out that in the 
same way the segregation of one pair of chromosomes 
is probably independent of the segregation of the 
other pairs. 
It was obvious from the beginning, however, that 
there was one essential requirement of the chromo- 
some view, namely, that all the factors carried by 
the same chromosome should tend to remain together. 
Therefore, since the number of inheritable characters 
may be large in comparison with the number of pairs 
of chromosomes, we should expect actually to find 
not only the independent behavior of pairs, but also 
cases in which characters are linked together in groups 
in their inheritance. Even in species where a limited 
